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1.. SPDX-License-Identifier: GPL-2.02 3=================================4Megaraid Common Management Module5=================================6 7Overview8--------9 10Different classes of controllers from LSI Logic accept and respond to the11user applications in a similar way. They understand the same firmware control12commands. Furthermore, the applications also can treat different classes of13the controllers uniformly. Hence it is logical to have a single module that14interfaces with the applications on one side and all the low level drivers15on the other.16 17The advantages, though obvious, are listed for completeness:18 19 i. Avoid duplicate code from the low level drivers.20 ii. Unburden the low level drivers from having to export the21 character node device and related handling.22 iii. Implement any policy mechanisms in one place.23 iv. Applications have to interface with only module instead of24 multiple low level drivers.25 26Currently this module (called Common Management Module) is used only to issue27ioctl commands. But this module is envisioned to handle all user space level28interactions. So any 'proc', 'sysfs' implementations will be localized in this29common module.30 31Credits32-------33 34::35 36 "Shared code in a third module, a "library module", is an acceptable37 solution. modprobe automatically loads dependent modules, so users38 running "modprobe driver1" or "modprobe driver2" would automatically39 load the shared library module."40 41- Jeff Garzik (jgarzik@pobox.com), 02.25.2004 LKML42 43::44 45 "As Jeff hinted, if your userspace<->driver API is consistent between46 your new MPT-based RAID controllers and your existing megaraid driver,47 then perhaps you need a single small helper module (lsiioctl or some48 better name), loaded by both mptraid and megaraid automatically, which49 handles registering the /dev/megaraid node dynamically. In this case,50 both mptraid and megaraid would register with lsiioctl for each51 adapter discovered, and lsiioctl would essentially be a switch,52 redirecting userspace tool ioctls to the appropriate driver."53 54- Matt Domsch, (Matt_Domsch@dell.com), 02.25.2004 LKML55 56Design57------58 59The Common Management Module is implemented in megaraid_mm.[ch] files. This60module acts as a registry for low level hba drivers. The low level drivers61(currently only megaraid) register each controller with the common module.62 63The applications interface with the common module via the character device64node exported by the module.65 66The lower level drivers now understand only a new improved ioctl packet called67uioc_t. The management module converts the older ioctl packets from the older68applications into uioc_t. After driver handles the uioc_t, the common module69will convert that back into the old format before returning to applications.70 71As new applications evolve and replace the old ones, the old packet format72will be retired.73 74Common module dedicates one uioc_t packet to each controller registered. This75can easily be more than one. But since megaraid is the only low level driver76today, and it can handle only one ioctl, there is no reason to have more. But77as new controller classes get added, this will be tuned appropriately.78